The type 1 receptor for insulin-like growth factors (IGF-IR), when activated by its ligands (IGF- I, IGF-II and insulin at supraphysiological concentrations) has at least 3 important biological activities; 1) it is mitogenic; 2) it regulates the establishment and maintenance of the transformed phenotype; and 3) it protects cells from apoptosis. This grant application focuses on the first two activities, which are partially overlapping, with greater emphasis on the transforming activity. Recent evidence from several laboratories have indicated that a functional IGF- IR plays a crucial role in transformation (colony formation in soft agar) and/or tumorigenesis. The basic observation was that mouse embryo cells with a targeted disruption of the IGF-IR genes are refractory to transformation by several oncogenes and other transforming agents. Conversely, a decrease in the number of IGF-IRs reverses the transformed phenotype. The laboratory is exploring the mechanism by which the IGF- IR regulates the establishment and maintenance of the transformed phenotype, with the long term goal of identifying the signaling pathways involved. In order to eventually reach that goal, the present application deals with the domains of the IGF-IR and with its immediate substrates that are required for the transforming signal. While the ras pathway is certainly involved in the transforming process, recent evidence indicates that other, ras-independent pathways must also be activated. The experiments are designed to define the receptor domains required for transformation, the role of IRS-1 (especially in relation to the SV40 T antigen), and the cloning of substrates specifically interacting with the transforming domains of the IGF-1R. Although the proposed project focuses on the IGF-1R, the information that would be generated could be extremely valuable in understanding the pathways of transformation in other systems as well, and the quasi-unique possibility of separating the pathway of transformation from the pathway of mitogenesis.